Preparation method of diameter-adjustable aramid nanofiber

Abstract

The invention discloses a preparation method of diameter-adjustable aramid nanofibers, and belongs to the technical field of polymer nanomaterials. The method comprises the following steps: heating calcium chloride and polyvinylpyrrolidone at 100 DEG C to dissolve in N-methyl pyrrolidone, cooling the system to 0-5 DEG C by using an ice-water bath, sequentially adding p-phenylenediamine and paraphthaloyl chloride, controlling the temperature of the system to be below 50 DEG C in the reaction process, reacting for 1.5 hours, and stopping stirring to obtain a PPTA solution; the preparation method comprises the following steps: diluting a PPTA solution with N-methyl pyrrolidone to obtain a PPTA diluent, putting the PPTA diluent in a high-speed dispersion machine, adding n-hexane while dispersing, and dispersing to obtain an ANFs dispersion liquid; the ANFs dispersion liquid is subjected to vacuum suction filtration, and aramid nanofibers of different sizes are obtained. The production process is simple, the cost is low, the aramid nanofibers with different sizes can be prepared according to different application scenes, and the method is a brand-new method for preparing the aramid nanofibers with different sizes and has a good industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer nanomaterials, and in particular relates to a method for preparing aramid nanofibers with adjustable diameter. Background Art

[0002] Para-aramid (PPTA), full name poly(p-phenylene terephthalamide), is a linear polymer whose main chain is alternately connected by amide groups and para-substituted benzene rings. Adjacent molecular chains are connected by a large number of hydrogen bonds and are symmetrically stretched, with extremely high nematicity and high crystallinity. This unique structure gives the fiber extremely high axial mechanical strength. However, the conjugation effect of amide bonds and benzene rings leads to low activity of hydrogen atoms on the molecular chain, resulting in low surface wettability. In addition, the smooth surface of the fiber lacks active chemical groups, resulting in low interface bonding and poor dispersibility, which makes it a technical shortcoming in the composite material system as a reinforcing material.

[0003] Aramid nanofibers (ANFs) are a type of polymer nanofiber material. They not only inherit the excellent properties of traditional aramid fibers, such as high strength, high temperature resistance, and corrosion resistance, but also have a larger specific surface area and unique nanometer size. Compared with para-aramid fibers, ANFs have abundant amide groups on their surfaces, which help improve the interfacial bonding between the fibers and the matrix, thereby improving the overall performance of the composite material. To date, ANFs have been widely used in polymer reinforcement, battery separators, adsorption filtration, and supercapacitors.

[0004] The preparation methods of ANFs mainly include chemical cleavage method and polymerization dispersion method. The chemical cleavage method refers to placing aramid fiber in an alkaline solution of potassium hydroxide (KOH) / dimethyl sulfoxide (DMSO), mixing and stirring for 7-10 days, and finally obtaining ANFs with a diameter of 10-30nm. The ANFs prepared by this method have relatively uniform size and excellent mechanical properties, but due to the long preparation cycle and low efficiency, it is difficult to achieve large-scale production, which limits its industrial application. The polymerization dispersion method is to prepare PPTA by polymerization of active monomers, and then prepare ANFs with a diameter of 30-50nm through PPTA self-assembly. Compared with the chemical cleavage method, the polymerization dispersion method has higher efficiency and is currently the only way to achieve industrial production of ANFs. However, due to the large number of amide bonds between the PPTA molecular chains, there is a strong hydrogen bond between the molecules, which makes the size control of ANFs prepared by the polymerization dispersion method a major challenge. This problem limits the industrial application and potential of ANFs in advanced materials. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of single size and difficulty in precise control of current aramid nanofibers, and to provide a method for preparing aramid nanofibers with adjustable diameter.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing aramid nanofibers with adjustable diameter, the method comprising:

[0008] Step 1: Heat the cosolvent calcium chloride and the surfactant polyvinyl pyrrolidone at 100°C and dissolve them in N-methyl pyrrolidone, then cool the system to 0-5°C using an ice water bath, then add p-phenylenediamine and terephthaloyl chloride in sequence, control the system temperature below 50°C during the reaction, stop stirring after reacting for 1.5 hours, and obtain a PPTA solution;

[0009] Step 2: diluting the PPTA solution obtained in step 1 with N-methylpyrrolidone to obtain a PPTA dilution solution;

[0010] Step 3: placing the PPTA dilution obtained in step 2 under a high-speed disperser, adding n-hexane thereto during dispersion, and obtaining an ANFs dispersion after dispersion is completed;

[0011] Step 4: vacuum filtration the ANFs dispersion obtained in step 3 to obtain aramid nanofibers of different sizes;

[0012] Step 5: The aramid nanofibers obtained in step 4 are repeatedly washed with anhydrous ethanol and deionized water, and then vacuum dried to obtain pure aramid nanofibers.

[0013] Furthermore, in step 1, the molar concentration of p-phenylenediamine in the solution is 0.2 mol / L; the molar concentration of terephthaloyl chloride in the solution is 0.2-0.204 mol / L; the molar concentration of calcium chloride in the solution is 0.45-0.54 mol / L; and the mass fraction of polyvinyl pyrrolidone in the solution is 0.05-3wt%.

[0014] Furthermore, in step 2, the concentration of the PPTA diluent is 2wt% to 0.5wt%.

[0015] Furthermore, in step three, the volume ratio of n-hexane to PPTA diluent is 1:1; the speed of the high-speed disperser is 6000-8000 rpm, the dispersion temperature is room temperature, and the dispersion time is 5 minutes.

[0016] Furthermore, in step 4, the filter membrane used in the vacuum filtration is a nylon filter membrane with a mesh size of 200 to 500.

[0017] Furthermore, in step five, the washing times are 3 to 5 times; the drying temperature is 60 to 80° C.; and the drying time is 24 hours.

[0018] Compared with the prior art, the present invention has the following advantages: The present invention proposes a method for preparing aramid nanofibers of different diameters by adding polyvinyl pyrrolidone as a surfactant during the synthesis of PPTA, which has the following advantages: first, there are a large number of amide bonds in the polyvinyl pyrrolidone molecular chain, which can produce hydrogen bonds with PPTA molecules, thereby effectively regulating the aggregation behavior of PPTA molecules and preventing PPTA from prematurely aggregating and precipitating to affect the molecular weight, such as Figure 4 As shown in the figure, the molecular weight of PPTA is increased after adding polyvinyl pyrrolidone. Secondly, the hydrogen bonding between polyvinyl pyrrolidone and PPTA molecules can also regulate the self-assembly process of PPTA, thereby achieving the regulation of the diameter of aramid nanofibers. Polyvinyl pyrrolidone is environmentally friendly and non-toxic, easily soluble in water, and can be removed by washing, so it will not affect the heat resistance of ANFs. Figure 5 The ANFs prepared by the method shown in the figure have excellent heat resistance. The method of the present invention can prepare aramid nanofibers of 50 to 200 nm by controlling the amount of polyvinyl pyrrolidone. The present invention has a simple production process and low cost. Aramid nanofibers of different sizes can be prepared according to different application scenarios. It is a new method for preparing aramid nanofibers of different sizes and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an electron microscope image of the aramid nanofiber (average diameter 140 nm) in Example 1, with a scale of 600 nm;

[0020] Figure 2 This is an electron microscope image of the aramid nanofiber (average diameter 80 nm) in Example 2, with a scale of 600 nm;

[0021] Figure 3 This is an electron microscope image of the aramid nanofiber (average diameter 50 nm) in Example 3, with a scale of 600 nm;

[0022] Figure 4 This is the change diagram of PPTA molecular weight under different polyvinyl pyrrolidone contents;

[0023] Figure 5 Thermogravimetric analysis of ANFs prepared at different polyvinyl pyrrolidone contents. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0025] Example 1

[0026] Add 100mL N-methylpyrrolidone to a 250mL three-necked flask, add 5g of polymerization aid calcium chloride and 0.05g of surfactant polyvinylpyrrolidone under nitrogen protection and stirring, and heat to 100°C to completely dissolve it. Then use an ice-water bath to reduce the system to 5°C and add 2.163g of p-phenylenediamine. After it is completely dissolved, add 4.101g of terephthaloyl chloride powder and maintain high-speed stirring (1500r / min) for polymerization. Keep an ice-water bath during the polymerization process to maintain the system temperature at no more than 50°C. After 1.5h of reaction, stop the reaction. Then take out 4g of PPTA solution and add 200mL of N-methylpyrrolidone to it, set the high-speed homogenizer speed to 8000r / min, and homogenize for 5min. Add 200mL of n-hexane to the PPTA diluent, set the high-speed homogenizer speed to 6000r / min, and homogenize for 5min. Filter the homogenized system to obtain aramid nanofibers and filtrate. The obtained aramid nanofibers were washed and filtered three times with a large amount of ethanol and deionized water, and finally the filtered products were dried in a vacuum drying oven at 60° C. for 24 hours. Scanning electron microscopy showed that the average diameter of the prepared nanofibers was 140 nm.

[0027] Example 2

[0028] Add 100mL N-methylpyrrolidone to a 250mL three-necked flask, add 5g of polymerization aid calcium chloride and 0.1g of surfactant polyvinylpyrrolidone under nitrogen protection and stirring, and heat to 100°C to completely dissolve it. Then use an ice-water bath to reduce the system to 5°C and add 2.163g of p-phenylenediamine. After it is completely dissolved, add 4.101g of terephthaloyl chloride powder and maintain high-speed stirring (1500r / min) for polymerization. Keep an ice-water bath during the polymerization process to maintain the system temperature at no more than 50°C. After 1.5h of reaction, stop the reaction. Then take out 4g of PPTA solution, add 200mL of N-methylpyrrolidone to it, set the high-speed homogenizer speed to 8000r / min, and homogenize for 5min. Add 200mL of n-hexane to the PPTA diluent, set the high-speed homogenizer speed to 7000r / min, and homogenize for 5min. Filter the homogenized system to obtain aramid nanofibers and filtrate. The obtained aramid nanofibers were washed and filtered three times with a large amount of ethanol and deionized water, and finally the filtered products were dried in a vacuum drying oven at 60° C. for 24 hours. Scanning electron microscopy showed that the average diameter of the prepared nanofibers was 80 nm.

[0029] Example 3

[0030] Add 100mL N-methylpyrrolidone to a 250mL three-necked flask, add 5g of polymerization aid calcium chloride and 0.3g of surfactant polyvinylpyrrolidone under nitrogen protection and stirring, and heat to 100°C to completely dissolve it. Then use an ice-water bath to reduce the system to 5°C and add 2.163g of p-phenylenediamine. After it is completely dissolved, add 4.101g of terephthaloyl chloride powder and maintain high-speed stirring (1500r / min) for polymerization. Keep an ice-water bath during the polymerization process to maintain the system temperature at no more than 50°C. After 1.5h of reaction, stop the reaction. Then take out 4g of PPTA solution, add 200mL of N-methylpyrrolidone to it, set the speed of the high-speed homogenizer to 8000r / min, and homogenize for 5min. Add 200mL of n-hexane to the PPTA diluent, set the speed of the high-speed homogenizer to 8000r / min, and homogenize for 5min. Filter the homogenized system to obtain aramid nanofibers and filtrate. The obtained aramid nanofibers were washed and filtered three times with a large amount of ethanol and deionized water, and finally the filtered products were dried in a vacuum drying oven at 60° C. for 24 hours. Scanning electron microscopy showed that the average diameter of the prepared nanofibers was 50 nm.

[0031] Example 4

[0032] Add 100mL N-methylpyrrolidone to a 250mL three-necked flask, add 5g of polymerization aid calcium chloride and 3g of surfactant polyvinylpyrrolidone under nitrogen protection and stirring, and heat to 100°C to completely dissolve it. Then use an ice-water bath to reduce the system to 5°C and add 2.163g of p-phenylenediamine. After it is completely dissolved, add 4.101g of terephthaloyl chloride powder and maintain high-speed stirring (1500r / min) for polymerization. Keep an ice-water bath during the polymerization process to maintain the system temperature not exceeding 50°C. After 1.5h of reaction, stop the reaction. Then take out 4g of PPTA solution, add 200mL of N-methylpyrrolidone to it, set the high-speed homogenizer speed to 8000r / min, and homogenize for 5min. Add 200ml of n-hexane to the PPTA diluent, set the high-speed homogenizer speed to 8000r / min, and homogenize for 5min. Filter the homogenized system to obtain aramid nanofibers and filtrate. The obtained aramid nanofibers were washed and filtered three times with a large amount of ethanol and deionized water, and finally the filtered products were dried in a vacuum drying oven at 60° C. for 24 hours. Scanning electron microscopy showed that the average diameter of the prepared nanofibers was 90 nm.

Claims

1. A method for preparing aramid nanofibers with adjustable diameter, characterized in that: The method is: Step 1: Heat the cosolvent calcium chloride and the surfactant polyvinyl pyrrolidone at 100°C and dissolve them in N-methyl pyrrolidone, then cool the system to 0-5°C using an ice water bath, then add p-phenylenediamine and terephthaloyl chloride in sequence, control the system temperature below 50°C during the reaction, stop stirring after reacting for 1.5 hours, and obtain a PPTA solution; Step 2: diluting the PPTA solution obtained in step 1 with N-methylpyrrolidone to obtain a PPTA dilution solution; Step 3: placing the PPTA dilution obtained in step 2 under a high-speed disperser, adding n-hexane thereto during dispersion, and obtaining an ANFs dispersion after dispersion is completed; Step 4: vacuum filtration the ANFs dispersion obtained in step 3 to obtain aramid nanofibers of different sizes; Step 5: The aramid nanofibers obtained in step 4 are repeatedly washed with anhydrous ethanol and deionized water, and then vacuum dried to obtain pure aramid nanofibers.

2. The method for preparing aramid nanofibers with adjustable diameter according to claim 1, characterized in that: In step 1, the molar concentration of p-phenylenediamine in the solution is 0.2 mol / L; the molar concentration of terephthaloyl chloride in the solution is 0.2-0.204 mol / L; the molar concentration of calcium chloride in the solution is 0.45-0.54 mol / L; and the mass fraction of polyvinyl pyrrolidone in the solution is 0.05-3wt%.

3. The method for preparing aramid nanofibers with adjustable diameter according to claim 1, characterized in that: In step 2, the concentration of the PPTA diluent is 2wt% to 0.5wt%.

4. The method for preparing aramid nanofibers with adjustable diameter according to claim 1, characterized in that: In step 3, the volume ratio of n-hexane to PPTA diluent is 1:1; the speed of the high-speed disperser is 6000-8000 rpm, the dispersion temperature is room temperature, and the dispersion time is 5 minutes.

5. The method for preparing aramid nanofibers with adjustable diameter according to claim 1, characterized in that: In step 4, the filter membrane used for vacuum filtration is a nylon filter membrane with a mesh size of 200 to 500.

6. The method for preparing aramid nanofibers with adjustable diameter according to claim 1, characterized in that: In step 5, the washing times are 3 to 5 times; the drying temperature is 60 to 80° C.; and the drying time is 24 hours.

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